Ellipsoidal UHPs can generate great brightness and high luminance, thus are widely used as the main lighting source on projectors or optical instruments. In general, the ellipsoidal lamp consists of a reflection hood 10 formed in a half-ellipsoidal shape and a burner 20 (Referring to FIGS. 1 and 2). The reflection hood 10 has a plated surface 11 (formed by a high reflective material) on one side facing the ellipsoidal focal point. The burner 20 is a UHP including a bulb 21 filled with mercury and inertial gases to generate a high pressure (about 180–250 atm.) when subject to arc discharge, two metal electrodes 22b and 22a (usually are tungsten electrodes) connecting respectively to a front foil 23 and a back foil 24 made of metal (usually molybdenum), and a leading wire 25 connecting to a tip wire 251 to couple with the front foil 23 to supply electricity. The interval of the two electrodes of the bulb 21 is located on the first focal point of the reflection hood 10. On the second focal point there is an integrated rod 26. Light emitting from the bulb 21 mostly are reflected by the plated surface 11 to the integrated rod 26 which allows the light focused on the second focal point to become uniform.
The bulb 21 is made from amorphous quartz glass durable to temperature about 1300° C. Temperature higher than that transforms the material of the bulb 21 to crystallized quartz glass and will result in decreasing of the glass transparency. And the temperature of the bulb 21 will increase and result in deformation and wall-thinning of the bulb 21 that will finally cause the bulb 21 to blast. The optimum operation temperature of the bulb 21 is about 850–950° C. At a temperature lower than that, mercury circulation in the bulb is not desirable and the bulb 21 will gradually darken, and the risk of blast also exists. Hence temperature control of the bulb 21 is very important. Uneven temperature will cause uneven thermal stress and result in blast or damage of the bulb 21. In general, the temperatures at a bulb top 211 and a bulb bottom 212 on two sides of the bulb 21 are used to determine whether the operation temperature is in the proper range. In addition, the electric connection points of the front foil 23 and the neighboring elements such as the tip wire 251 and a first connection point 252 also tend to oxidize under high temperature, and that also affects the life span of the UHP.
Therefore heat dissipation of the UHP is an important issue. A conventional heat dissipation method (referring to FIG. 2) is to channel heat dissipation airflow through a blower duct 30 to the hot spots that require cooling. The hot spots include the bulb top 211, and the electric connection points of the front foil 23 and the neighboring elements such as the tip wire 251 and the first connection point 252. To avoid blocking the reflection light reflected by the plated surface 11, the blower duct 30 is located on the periphery of the reflection hood 10 (especially a straight line-1 extended from the edge of the plated surface 11 along the light exit projecting direction) so that light gathering of the integrated rod 26 is not affected. Otherwise the blower duct 30 will block the reflection light from the plated surface 11 and affect the optical efficiency of the system.
The airflow for heat dissipation is provided by a blower 40. Due to the airflow poured out from the blower 40 is scattering, the blower duct 30 is provided to converge the airflow and direct the airflow to the hot spots of the burner 20 to disperse heat. Theoretically, the closer the blower duct 30 from the hot spots, the better the heat dissipation effect becomes. But the optical design requires to converge as mush of the reflection light from the reflection hood 10 to the integrated rod as possible, it is not desirable to have any thing blocking the light exit of the burner 20. Hence the airflow outlet of the conventional blower duct 30 is usually located on the outer side of the reflection hood 10 (referring to FIG. 3).
Due to the front end of the airflow outlet of the blower duct 30 is far away from the hot spots, the output airflow often cannot cover or concentrate on the entire burner 20. To resolve the heat dissipation problem of the bulb, the airflow volume of the blower 40 has to increase. In the high power projector (200W or more), the blower 40 generates a great noise even louder than the axial fan. Moreover, boosting the airflow volume of the blower 40 not only increases the noise of the system, increasing the rotational speed also affects the life span of the blower 40.
Furthermore, the conventional blower duct 30 is separated from the ellipsoidal lamp. Airflow leakage occurs between the blower duct 30 and the ellipsoidal lamp. This results in circulation of heated air and affects heat dissipation.